JPWO2016152280A1 - Separation membrane for gas treatment containing acid gas and method for producing separation membrane for gas treatment containing acid gas - Google Patents

Abstract

In addition to optimizing the intermediate layer provided on the support, the mixed gas containing acid gas and methane gas and / or nitrogen gas is treated and separated into respective gas components, and the acid gas or methane gas and / or nitrogen gas is efficiently removed. An acid gas-containing separation membrane for gas treatment that can be obtained is provided. An acidic gas-containing gas treatment separation membrane obtained by laminating an intermediate layer and a separation layer on an inorganic porous support, wherein the intermediate layer comprises a tetraalkoxysilane (A1) and a hydrocarbon group-containing trialkoxysilane ( B1) and a polysiloxane network structure in which the blending ratio (A1 / B1) is adjusted to 30/70 to 99.9 / 0.1 by weight, and the separation layer is composed of tetraalkoxysilane (A2) and carbonized A polysiloxane network structure in which the blending ratio (A2 / B2) with the hydrogen group-containing trialkoxysilane (B2) is adjusted to 0/100 to 70/30 by weight is included.

Description

  The present invention relates to an acid gas-containing gas treatment separation membrane that treats a mixed gas containing an acid gas and other gases and separates them into respective gas components, and a method for producing the same.

  The use of methane gas has been studied as an energy resource to replace oil. Methane gas is mainly obtained as natural gas, but in recent years, methane gas has been used to produce methane hydrate, deep-sea methane hydrate, digestion gas generated when biological waste is processed biologically, off-gas generated as a by-product in petroleum refining, etc. It is considered to be a source. However, these methane gas sources may contain acidic gas (carbon dioxide, hydrogen sulfide, etc.) in addition to methane gas. Therefore, in order to use a mixed gas containing acid gas and methane gas as a raw material for city gas or hydrogen used in fuel cells, either methane gas alone is separated from the mixed gas, or the concentration of methane gas in the mixed gas is changed. It is necessary to raise.

  Moreover, nitrogen gas and acid gas are contained in the exhaust gas discharged | emitted from a factory or a power plant. If the mixed gas containing the nitrogen gas and the acid gas is also appropriately treated and separated into the respective gas components, the utility value of the gas is increased. For example, if carbon dioxide, which is an acidic gas, can be efficiently recovered from exhaust gas from a factory, it can be commercialized as liquefied carbon dioxide gas.

  Since carbon dioxide can cause global warming, it is not desirable to release it directly into the atmosphere. Then, the carbon dioxide which generate | occur | produced in a factory or a power station, for example, the technique (Carbon dioxide Capture and Storage: CCS) which stores deeply in the ground is examined in various fields. In order to promote this CCS, it is desired to appropriately treat exhaust gas containing carbon dioxide.

Conventionally, as a technique for separating methane gas from a mixed gas containing carbon dioxide and methane gas, for example, by arranging separation membranes in two stages and allowing the mixed gas to pass through the separation membranes of each stage, other than methane gas in the mixed gas There is a methane concentrator that increases the concentration of methane gas by separating the gas in steps (see, for example, Patent Document 1). The methane concentrator of Patent Document 1 separates a gas A having a molecular diameter smaller than that of methane gas from a mixed gas. However, as a separation membrane, the permeability coefficient ratio A / methane between gas A and methane is 5 or more and gas A transmittance is using an inorganic porous membrane having a ^{1 × 10 -9 (mol · m} -2 · s -1 · Pa -1) or more properties. It is said that by using such a separation membrane, a gas having a high methane concentration can be recovered in a high yield.

  In obtaining high-concentration methane gas from a mixed gas containing carbon dioxide and methane gas, if carbon dioxide is separated from the mixed gas, the concentration of methane gas in the mixed gas will be relatively increased. Methane gas can be obtained. As a technique for separating carbon dioxide from a mixed gas, in a separation membrane made of an amorphous oxide having a plurality of pores formed by cyclic siloxane bonds, nitrogen (N) having basicity in the side chain of Si and There has been a gas separation filter using a functional group containing silicon (Si) combined (for example, see Patent Document 2). According to the gas separation filter of Patent Document 2, acidic gas such as carbon dioxide efficiently passes through narrow pores, so that separation performance can be improved.

JP 2008-260739 A JP 2000-279773 A

In order to efficiently separate the mixed gas containing methane gas and / or nitrogen gas and carbon dioxide into respective gas components, for example, a separation membrane capable of efficiently transmitting carbon dioxide contained in the mixed gas is used. Need to develop. In this regard, the methane concentrator of Patent Document 1 uses a separation membrane that separates the gas A having a molecular diameter smaller than that of methane gas, and the gas A includes carbon dioxide. Then, according to an embodiment of the document, as permeability coefficient ratio _CO 2 / CH ₄ of carbon dioxide and methane, the value of 3.3 to 20 is shown. However, at such a permeation coefficient ratio, the loss of methane gas is large, and if a complicated apparatus configuration such as a separation membrane having two stages as in Patent Document 1 and recirculation of non-permeate gas is used, it is a practical level. However, it was difficult to concentrate methane gas sufficiently.

  The gas separation filter of Patent Document 2 intends to improve the carbon dioxide separation performance by introducing a functional group containing basic nitrogen (N) and silicon (Si) on the surface of the separation membrane. It is. In order to exhibit sufficient carbon dioxide separation performance, it is important to form a uniform membrane while introducing a sufficient number of functional groups on the surface of the separation membrane. However, in the separation membrane of Patent Document 2, the number of functional groups that can be introduced is determined by the molecular structure of the raw material (the number of reaction sites), and the carbon dioxide separation performance is improved only by improving the separation membrane itself. Has its limits. In addition, when the number of functional groups introduced into the separation membrane increases, steric hindrance is likely to occur in the molecular structure, which may adversely affect uniform membrane formation.

  The separation membrane used in Patent Document 1 and Patent Document 2 is prepared by applying a liquid (sol-like) separation membrane forming material to a support and heat-treating it. Here, in order to improve the film-forming property of the separation membrane on the support, an intermediate layer is provided in advance on the support. In this case, it is important for the intermediate layer to properly select the weight of the intermediate layer forming material and the support in consideration of the relationship between the constituent material of the separation membrane and the support. However, in Patent Document 1 and Patent Document 2, the technical idea of selecting the intermediate layer forming material in consideration of the constituent material of the separation membrane is not seen, and the basis weight on the support is not examined. .

  The present invention has been made in view of the above-described problems, and optimizes the intermediate layer provided on the support and treats a mixed gas containing acid gas and methane gas and / or nitrogen gas to thereby provide each gas component. It is an object of the present invention to provide an acid gas-containing gas treatment separation membrane capable of efficiently obtaining acid gas or methane gas and / or nitrogen gas and a method for producing the same.

The characteristic structure of the separation membrane for acid gas-containing gas treatment according to the present invention for solving the above problems is as follows:
A separation membrane for gas treatment containing an acidic gas, wherein an intermediate layer and a separation layer are laminated on an inorganic porous support,
In the intermediate layer, the blending ratio (A1 / B1) of the tetraalkoxysilane (A1) and the hydrocarbon group-containing trialkoxysilane (B1) was adjusted to 30/70 to 99.9 / 0.1 by weight. A polysiloxane network obtained by a sol-gel reaction of alkoxysilane,
The separation layer is an alkoxysilane sol in which the mixing ratio (A2 / B2) of the tetraalkoxysilane (A2) to the hydrocarbon group-containing trialkoxysilane (B2) is adjusted to 0/100 to 70/30 by weight ratio. -Comprising a polysiloxane network obtained by gel reaction,
The blending ratio (A1 / B1) is set to be larger than the blending ratio (A2 / B2).

According to the acidic gas-containing gas treatment separation membrane of this configuration, the polysiloxane network structure contained in the intermediate layer contains hydrocarbon groups derived from hydrocarbon group-containing trialkoxysilane, which is one of the raw materials. It has more flexibility than a general polysiloxane network. Therefore, the intermediate layer can improve the overall flexibility and flexibility while maintaining a certain degree of rigidity by the tetraalkoxysilane which is another raw material. When the flexibility of the intermediate layer is improved, the film formability of the intermediate layer is improved. Thereby, the crack and peeling of the intermediate layer are prevented, and the amount of the raw material liquid of the separation layer penetrating into the inorganic porous support is reduced. As a result, an increase in the thickness of the separation layer is suppressed, and an acidic gas-containing gas treatment separation membrane excellent in gas permeability can be obtained.
Moreover, the polysiloxane network structure contained in each of the intermediate layer and the separation layer is composed of materials of the same system except that the blending ratio of tetraalkoxysilane and hydrocarbon group-containing trialkoxysilane is different. , Have high affinity for each other. Therefore, when an intermediate layer is formed on the surface of the inorganic porous support and a separation layer is formed thereon, no interfacial delamination or cracking occurs between the intermediate layer and the separation layer, and the two adhere firmly. A stable separation membrane for acid gas-containing gas treatment can be configured. When a mixed gas containing acidic gas and methane gas and / or nitrogen gas is passed through this acidic gas-containing gas treatment separation membrane, the separation layer is derived from the hydrocarbon group-containing trialkoxysilane rather than the intermediate layer. Since it contains many hydrocarbon groups, the acidic gas in the mixed gas is selectively attracted to the separation layer and permeates the separation membrane as it is. As a result, the methane gas component and / or nitrogen gas component in the mixed gas is concentrated, and high-concentration methane gas and / or nitrogen gas can be obtained efficiently. Moreover, since the acidic gas that has passed through the separation membrane is also highly pure, the utility value is high.

In the separation membrane for treatment of acid gas-containing gas according to the present invention,
The tetraalkoxysilane is tetramethoxysilane or tetraethoxysilane,
The hydrocarbon group-containing trialkoxysilane is preferably one in which an alkyl group having 1 to 6 carbon atoms or a phenyl group is bonded to the Si atom of trimethoxysilane or triethoxysilane.

  According to the separation membrane for acid gas-containing gas treatment of this configuration, the intermediate layer has a balance between rigidity and flexibility because the significant combination of tetraalkoxysilane and hydrocarbon group-containing trialkoxysilane is selected. Thus, the separation layer has excellent acid gas selectivity and gas permeability.

In the separation membrane for treatment of acid gas-containing gas according to the present invention,
It is preferable that a metal salt having an affinity for acidic gas is added to the separation layer.

  According to the separation membrane for acid gas-containing gas treatment of this configuration, by adding a metal salt having an affinity for acid gas to the separation layer, the acid gas selectivity due to the hydrocarbon group contained in the separation layer, and the metal salt The affinity with the acidic gas by the synergistic effect exerts synergistically, and the separation performance of the acidic gas in the acidic gas-containing gas processing separation membrane can be further enhanced.

In the separation membrane for treatment of acid gas-containing gas according to the present invention,
The metal salt is an acetate, nitrate, carbonate, borate, or phosphoric acid of at least one metal selected from the group consisting of Li, Na, K, Cs, Mg, Ca, Ni, Fe, and Al. A salt is preferred.

  According to the acidic gas-containing gas treatment separation membrane of this configuration, the above-described significant metal salt is selected as the metal salt having affinity with the acidic gas, so that the separation performance of acidic gas can be further enhanced.

In the separation membrane for treatment of acid gas-containing gas according to the present invention,
The weight of the intermediate layer is 0.1 to 4.0 mg / cm ² ,
The basis weight of the separation layer is preferably 0.1 to 3.0 mg / cm ² .

  According to the separation membrane for acid gas-containing gas treatment of this configuration, the basis weight of the intermediate layer and the separation layer is set in the above appropriate range, so that the stable structure of the intermediate layer and the excellent acidity by the separation layer Gas selectivity and gas permeability can be achieved at a high level.

In the separation membrane for treatment of acid gas-containing gas according to the present invention,
The inorganic porous support preferably has fine pores of 4 to 200 nm.

  According to the separation membrane for acid gas-containing gas treatment of this configuration, since the inorganic porous support has the fine pores of the appropriate size, the raw material for the intermediate layer and the separation layer on the inorganic porous support A certain level of gas permeability can be ensured while suppressing the amount of penetration of the liquid.

In the separation membrane for treatment of acid gas-containing gas according to the present invention,
The distance that the alkoxysilane penetrates in the depth direction from the surface of the inorganic porous support is preferably 50 μm or less.

  According to the acidic gas-containing gas treatment separation membrane of this configuration, since the amount of alkoxysilane (raw material liquid) permeating into the inorganic porous support is suppressed to a range of 50 μm or less from the surface, the inorganic porous The micropores of the support are not clogged excessively, and the gas passage amount (mixed gas treatment amount) can be maintained over a long period of time. Moreover, since the usage-amount of a raw material can be reduced, it can also contribute to the reduction of the manufacturing cost of a separation membrane.

In order to solve the above-mentioned problems, the characteristic configuration of the method for producing a separation membrane for acid gas-containing gas treatment according to the present invention is as follows:
(A) Alkoxysilane whose blending ratio (A1 / B1) of tetraalkoxysilane (A1) to hydrocarbon group-containing trialkoxysilane (B1) is adjusted to 30/70 to 99.9 / 0.1 by weight ratio , An acid catalyst, water, and a first mixed liquid in which an organic solvent is mixed, and a mixing ratio (A2 / B2) of the tetraalkoxysilane (A2) to the hydrocarbon group-containing trialkoxysilane (B2) is 0 / weight ratio. A second mixed solution in which an alkoxysilane adjusted to 100 to 70/30, an acid catalyst, water, and an organic solvent are mixed (wherein the blending ratio (A1 / B1) is based on the blending ratio (A2 / B2)). A preparation step for preparing a large set),
(B) a first coating step of coating the first mixed liquid on the surface of the inorganic porous support;
(C) an intermediate layer forming step of heat-treating the inorganic porous support after the first coating step is completed, and forming an intermediate layer including a polysiloxane network structure on the surface of the inorganic porous support;
(D) a second coating step of coating the second mixed solution on the intermediate layer;
(E) a separation layer forming step of heat-treating the inorganic porous support having undergone the second coating step to form a separation layer containing a polysiloxane network structure on the intermediate layer;
It is to include.

  According to the method for producing an acid gas-containing gas treatment separation membrane of this configuration, the same excellent effects as those of the acid gas-containing gas treatment separation membrane described above are exhibited. That is, by improving the flexibility of the intermediate layer and improving the film formability, the intermediate layer is prevented from being cracked or peeled off, and the amount of raw material liquid permeating into the inorganic porous support is reduced. As a result, an increase in the thickness of the separation layer can be suppressed, and an acidic gas-containing gas treatment separation membrane excellent in gas selectivity and gas permeability can be obtained. Moreover, since the intermediate layer and the separation layer are made of the same material having different compounding ratios between the tetraalkoxysilane and the hydrocarbon group-containing trialkoxysilane, no interfacial peeling or cracking occurs between the layers. A stable separation membrane for acid gas-containing gas treatment can be configured.

In the method for producing an acid gas-containing separation membrane for gas treatment according to the present invention,
In the preparation step, the ratio (W1 / W2) between the amount of water (W1) used for preparing the first mixed solution and the amount of water (W2) used for preparing the second mixed solution is mol. It is preferably set to 10 to 20 in terms of conversion.

  According to the method for producing an acid gas-containing gas treatment separation membrane of this configuration, the amount of water (W1) used for preparing the first mixed solution and the amount of water (W2) used for preparing the second mixed solution. And the ratio (W1 / W2) is set in the above appropriate range, so that the intermediate layer having a stable structure on the surface of the inorganic porous support and the separation layer excellent in gas selectivity and gas permeability And can be reliably formed.

In the method for producing an acid gas-containing separation membrane for gas treatment according to the present invention,
In the preparation step, when preparing the first mixed liquid, it is preferable to mix water in a plurality of times.

  According to the method for producing a separation membrane for acid gas-containing gas treatment of this configuration, when preparing the first mixed liquid, when water is divided and mixed several times, it is formed through the first coating step and the intermediate layer forming step. In the polysiloxane network structure, the hydrolysis reaction surely proceeds to polymerize and stays in the vicinity of the surface of the inorganic porous support. As a result, the amount of penetration of the second mixed liquid into the inorganic porous support is reduced in the second coating step, and the film forming property of the separation layer in the separation layer forming step is improved.

It is a schematic block diagram of the gas permeation rate measuring apparatus used for the separation performance confirmation test. It is a graph which shows Si distribution of the separation membrane for acidic gas containing gas processing produced by changing the addition amount of the water in a 1st liquid mixture. It is a graph which shows Si distribution of the separation membrane for acid gas containing gas processing produced by changing the addition conditions of the water in a 1st liquid mixture.

  Hereinafter, the embodiment regarding the manufacturing method of the separation membrane for acidic gas containing gas processing concerning this invention and the separation membrane for acidic gas containing gas processing is described. However, the present invention is not intended to be limited to the configuration described below.

<Separation membrane for acid gas containing gas treatment>
The separation membrane for treatment of acid gas-containing gas of the present invention uses a mixed gas containing acid gas and methane gas and / or nitrogen gas (hereinafter sometimes referred to as “acid gas-containing gas”) as a treatment target. However, in this embodiment, a mixed gas of acid gas and methane gas will be described as an example. Here, the acidic gas is a gas that shows acidity when dissolved in water, and examples thereof include carbon dioxide and hydrogen sulfide. In the present embodiment, carbon dioxide is assumed as the acidic gas, and the following description will be given. Accordingly, the acidic gas-containing gas treatment separation membrane of the present invention will be described as a carbon dioxide separation membrane for separating carbon dioxide, but a methane gas separation membrane for separating methane gas, a nitrogen gas separation membrane for separating nitrogen gas, or carbon dioxide It is also possible to configure as a carbon dioxide / (methane gas and / or nitrogen gas) separation membrane capable of simultaneously separating methane gas and / or nitrogen gas. Hereinafter, the separation membrane for treatment of acid gas-containing gas may be simply referred to as “separation membrane”.

  The separation membrane for acid gas-containing gas treatment is constituted by forming an intermediate layer on an inorganic porous support serving as a base, and further forming a separation layer thereon. Hereinafter, the inorganic porous support, the intermediate layer, and the separation layer will be described in detail.

[Inorganic porous support]
The inorganic porous support is made of, for example, a material such as silica-based ceramics, silica-based glass, alumina-based ceramics, stainless steel, titanium, or silver. Among these, alumina-based ceramics are suitable as a material for an inorganic porous support because they are excellent in heat resistance, easy to process, and relatively inexpensive. The inorganic porous support is provided with an inflow portion into which gas flows and an outflow portion from which gas flows out. For example, the gas inflow portion is an opening provided in the inorganic porous support, and the gas outflow portion is the outer surface of the inorganic porous support. It is also possible to use the outer surface of the inorganic porous support as a gas inflow portion and the opening provided in the inorganic porous support as a gas outflow portion. Since innumerable micropores are formed on the outer surface of the inorganic porous support, gas can flow from the entire outer surface. Examples of the configuration of the inorganic porous support include a cylindrical structure with a gas flow path inside, a circular pipe structure, a tubular structure, a spiral structure, and a large number of flow paths such as lotus holes in one element. Monolith structure provided, communication structure in which continuous pores that are intricately interlaced are formed, solid porous structure in which the porous body is formed into a columnar shape, hollow porous structure in which the porous body is formed into a cylindrical shape, Examples thereof include a honeycomb structure in which honeycomb structures are arranged in a tubular shape. Further, an inorganic porous support may be configured by preparing a solid flat plate or a bulk body made of an inorganic porous material and forming a gas flow path by hollowing out a part thereof. . The size of the fine pores of the inorganic porous support can be selected from the nm order to the μm order depending on the application, but is adjusted to, for example, 4 to 200 nm.

[Middle layer]
An intermediate | middle layer is provided in order to stabilize the surface of an inorganic porous support body, and to make it easy to form the below-mentioned separated layer. For example, when a liquid mixture (sol) containing a material for forming a separation layer, which will be described later, is directly applied to the surface of an inorganic porous support having a relatively large micropore size, the liquid mixture penetrates excessively into the micropores. In addition to the surface of the inorganic porous support, it may be difficult to form a separation layer. Therefore, by providing an intermediate layer on the surface of the inorganic porous support, the entrance of the micropores is narrowed by the intermediate layer, and the application of the mixed liquid becomes easy. Moreover, since the surface of the inorganic porous support is equalized by the intermediate layer, separation and cracking of the separation layer can be suppressed.

  The intermediate layer is configured to include a silane compound. The intermediate layer of the present embodiment is obtained by a sol-gel reaction of tetraalkoxysilane and hydrocarbon group-containing trialkoxysilane.

  Tetraalkoxysilane is a tetrafunctional alkoxysilane represented by the following formula (1).

A preferred tetraalkoxysilane in formula (1) is tetramethoxysilane (TMOS) in which R _{1 to} R ₄ are the same methyl group or tetraethoxysilane (TEOS) in which the same ethyl group is used.

  The hydrocarbon group-containing trialkoxysilane containing a hydrocarbon group is a trifunctional alkoxysilane represented by the following formula (2).

A preferred hydrocarbon group-containing trialkoxysilane is represented by the formula (2), in which R _{6 to} R ₈ are trimethoxysilane having the same methyl group or triethoxysilane having the same ethyl group to the Si atom of 1 to 6 carbon atoms. In which an alkyl group or a phenyl group is bonded. For example, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, pentyltrimethoxysilane, pentyltriethoxy Examples include silane, hexyltrimethoxysilane, hexyltriethoxysilane, phenyltrimethoxysilane, and phenyltriethoxysilane.

  When a tetraalkoxysilane of the formula (1) and a hydrocarbon group-containing trialkoxysilane of the formula (2) are subjected to a sol-gel reaction, for example, a polysiloxane network having a molecular structure represented by the following formula (3) A structure is obtained.

The hydrocarbon group-containing trialkoxysilane of formula (2), which is one of the raw materials of the polysiloxane network structure of formula (3), has different characteristics depending on the difference in R ₅ . For example, methyltrimethoxysilane or methyltriethoxysilane (having a hydrocarbon group with 1 carbon atom) has an affinity mainly for carbon dioxide, and the number of carbon atoms in the Si atom of trimethoxysilane or triethoxysilane Those having 2 to 6 alkyl groups or phenyl groups bonded thereto (hydrocarbon groups having 2 to 6 carbon atoms) mainly have affinity for methane gas. In synthesizing the polysiloxane network structure of the formula (3) from the reaction between the tetraalkoxysilane of the formula (1) and the hydrocarbon group-containing trialkoxysilane of the formula (2), the tetraalkoxysilane (this A) and hydrocarbon group-containing trialkoxysilane (referred to as B) are set to an optimum blending ratio, and it becomes possible to form a separation membrane having excellent carbon dioxide or methane gas separation performance. .

In forming the intermediate layer, the blending ratio (A1 / B1) of the tetraalkoxysilane (A1) and the hydrocarbon group-containing trialkoxysilane (B1) is 30/70 to 99.9 / 0.1 by weight ratio, The tetraalkoxysilane of the formula (1) and the hydrocarbon group-containing trialkoxysilane of the formula (2) are blended so that the ratio is preferably 60/40 to 99.9 / 0.1. In this case, since the intermediate layer contains a hydrocarbon group derived from a hydrocarbon group-containing trialkoxysilane, the intermediate layer is more flexible than a general network structure, and a certain degree of rigidity is maintained by the tetraalkoxysilane. However, overall flexibility and flexibility can be improved. As a result, the intermediate layer is stabilized, and the separation layer described later has good film formability. In the polysiloxane network structure of the formula (3), the hydrocarbon group R ₅ is present in the polysiloxane network structure and forms a certain organic-inorganic composite.

(Separation layer)
The separation layer has a function of selectively attracting and separating carbon dioxide from a mixed gas containing carbon dioxide and methane gas and / or nitrogen gas. The separation layer is obtained by a sol-gel reaction of tetraalkoxysilane and hydrocarbon group-containing trialkoxysilane.

The tetraalkoxysilane and the hydrocarbon group-containing trialkoxysilane are the tetraalkoxysilane represented by the above formula (1) and the hydrocarbon group-containing trialkoxysilane represented by the formula (2) used for forming the intermediate layer. Can be used. A preferred tetraalkoxysilane is the same as the intermediate layer, and in formula (1), R _{1 to} R ₄ are the same methyl group tetramethoxysilane (TMOS) or the same ethyl group tetraethoxysilane (TEOS). It is. The preferred hydrocarbon group-containing trialkoxysilane is the same as that of the intermediate layer, and in formula (2), R _{6 to} R ₈ are trimethoxysilane having the same methyl group or triethoxysilane having the same ethyl group. A C 1-6 alkyl group or phenyl group is bonded to a Si atom.

  Also in the separation layer, the molecular structure represented by the above-described formula (3) is obtained by causing a sol-gel reaction between the tetraalkoxysilane of the formula (1) and the hydrocarbon group-containing trialkoxysilane of the formula (2). A polysiloxane network structure is obtained. In forming the separation layer, the mixing ratio (A2 / B2) of the tetraalkoxysilane (A2) to the hydrocarbon group-containing trialkoxysilane (B2) is 0/100 to 70/30, preferably 40 / The tetraalkoxysilane of the formula (1) and the hydrocarbon group-containing trialkoxysilane of the formula (2) are blended so as to be 60 to 70/30. Further, when forming the intermediate layer and the separation layer, tetraalkoxysilane and carbonization are performed so that the blending ratio (A1 / B1) at the time of forming the intermediate layer is larger than the blending ratio (A2 / B2) at the time of forming the separation layer. A hydrogen group-containing trialkoxysilane is blended. In this case, since the separation layer contains more hydrocarbon groups derived from the hydrocarbon group-containing trialkoxysilane than the intermediate layer, the acidic gas in the mixed gas is selectively attracted to the separation layer, and the The acidic gas can be efficiently separated.

  It is preferable to add (dope) a metal salt having an affinity for carbon dioxide to the polysiloxane network structure of the above formula (3). Thereby, the metal salt is contained in the separation layer, and the separation performance of the separation membrane can be further enhanced. Of course, the metal salt can be added to the intermediate layer. As the metal salt, acetate, nitrate, carbonate, borate, or phosphoric acid of at least one metal selected from the group consisting of Li, Na, K, Cs, Mg, Ca, Ni, Fe, and Al Salt. Of these, magnesium nitrate or magnesium acetate is preferred. Since the above metal salts including magnesium nitrate have good affinity with carbon dioxide, they are effective in improving the separation efficiency of carbon dioxide. The method of adding the metal salt is performed, for example, by an impregnation method in which a polysiloxane network structure is immersed in an aqueous solution containing the metal salt, and the metal salt is impregnated alone or with other substances inside the polysiloxane network structure. However, a metal salt may be added in advance to the raw material of the polysiloxane network structure.

<Method for producing separation membrane for treatment of acid gas-containing gas>
The acidic gas-containing gas treatment separation membrane of the present invention is produced by the following steps (a) to (e). Hereinafter, each step will be described in detail.

(A) Preparatory process As a preparatory process, the compounding ratio (A1 / B1) of tetraalkoxysilane (A1) and hydrocarbon group containing trialkoxysilane (B1) is 30 / 70-99.9 / 0.1 by weight ratio. A first mixed solution is prepared by mixing the alkoxysilane, acid catalyst, water, and organic solvent prepared in the above step. The first liquid mixture is used in the “first coating step” of the next step. Each compounding amount of alkoxysilane (tetraalkoxysilane and hydrocarbon group-containing trialkoxysilane), acid catalyst, water, and organic solvent is based on 1 mol of the total amount of tetraalkoxysilane and hydrocarbon group-containing trialkoxysilane. The acid catalyst is preferably adjusted to 0.001 to 0.1 mol, water 0.5 to 60 mol, and organic solvent 5 to 60 mol. When the compounding amount of the acid catalyst is less than 0.001 mol, the hydrolysis rate becomes low and the time required for producing the separation membrane becomes long. When the compounding amount of the acid catalyst is more than 0.1 mol, the hydrolysis rate becomes excessive, and it becomes difficult to obtain a uniform separation membrane. When the amount of water is less than 0.5 mol, a sol-gel reaction product accompanied by a hydrolysis reaction does not grow sufficiently. When the amount of water is more than 60 mol, the film formability is deteriorated. When the blending amount of the organic solvent is less than 5 mol, the concentration of the first mixed solution becomes high and it becomes difficult to obtain a dense and uniform separation membrane. When the blending amount of the organic solvent is more than 60 mol, the concentration of the first mixed solution is lowered, the number of coating times (number of steps) of the mixed solution is increased, and the production efficiency is lowered. As the acid catalyst, for example, nitric acid, hydrochloric acid, sulfuric acid and the like are used. Of these, nitric acid or hydrochloric acid is preferred. As the organic solvent, for example, methanol, ethanol, propanol, butanol, benzene, toluene and the like are used. Of these, methanol or ethanol is preferred.

  When the first mixed solution is prepared, first, a sol-gel reaction in which tetraalkoxysilane repeats hydrolysis and polycondensation starts. As the tetraalkoxysilane, those described in the item “Separation membrane for treatment of acid gas-containing gas” can be used. For example, when tetraethoxysilane (TEOS) is used as an example of tetraalkoxysilane, the sol-gel reaction is considered to proceed as shown in Scheme 1 below. This scheme 1 is one model representing the progress of the sol-gel reaction, and does not always reflect the actual molecular structure as it is.

スキーム１によれば、初めに、テトラエトキシシランの一部のエトキシ基が加水分解され、脱アルコール化することによりシラノール基が生成する。ここで、第一混合液中で進行する加水分解反応を「第一加水分解反応」とする。テトラエトキシシランの一部のエトキシ基は加水分解されず、そのまま残存し得る。次いで、一部のシラノール基が近傍のシラノール基と会合し、脱水することにより重縮合する。その結果、シラノール基又はエトキシ基が残存したシロキサン骨格が形成される。上記の第一加水分解反応、及び脱水・重縮合反応は混合液系内で略均等に進行するため、シラノール基又はエトキシ基はシロキサン骨格中に略均等に分散した状態で存在する。この段階では、シロキサンの分子量はそれほど大きいものではなく、ポリマーよりもむしろオリゴマーの状態にある。従って、シラノール基又はエトキシ基含有シロキサンオリゴマーは、有機溶媒を含む第一混合液に溶解した状態にある。

According to Scheme 1, first, a part of ethoxy groups of tetraethoxysilane are hydrolyzed and dealcoholized to produce silanol groups. Here, the hydrolysis reaction proceeding in the first mixed solution is referred to as “first hydrolysis reaction”. Some ethoxy groups of tetraethoxysilane are not hydrolyzed and can remain as they are. Next, some silanol groups associate with neighboring silanol groups and are polycondensed by dehydration. As a result, a siloxane skeleton in which silanol groups or ethoxy groups remain is formed. Since the first hydrolysis reaction and the dehydration / polycondensation reaction proceed substantially evenly in the mixed liquid system, the silanol group or ethoxy group exists in a substantially uniformly dispersed state in the siloxane skeleton. At this stage, the molecular weight of the siloxane is not very high and is in an oligomer rather than a polymer. Therefore, the silanol group or ethoxy group-containing siloxane oligomer is in a state of being dissolved in the first mixed liquid containing the organic solvent.

  Next, the reaction between the siloxane oligomer and the hydrocarbon group-containing trialkoxysilane starts. As the hydrocarbon group-containing trialkoxysilane, those described in the item “Separation membrane for gas treatment containing acid gas” described above can be used. For example, when methyltriethoxysilane is used as an example of a hydrocarbon group-containing trialkoxysilane, the reaction is considered to proceed as shown in Scheme 2 below. Note that Scheme 2 is a model representing the progress of the reaction, and does not necessarily reflect the actual molecular structure as it is.

スキーム２によれば、シロキサンオリゴマーのシラノール基又はエトキシ基と、メチルトリエトキシシランのエトキシ基とが反応し、脱アルコール化することによりポリシロキサン結合が生成する。ここで、シロキサンオリゴマーのシラノール基又はエトキシ基は、上述のようにシロキサン骨格中に略均等に分散しているため、シロキサンオリゴマーのシラノール基又はエトキシ基とメチルトリエトキシシランのエトキシ基との反応（脱アルコール化）も略均等に進行すると考えられる。その結果、生成したポリシロキサン結合中にはメチルトリエトキシシラン由来のシロキサン結合が略均等に生成し、従って、メチルトリエトキシシラン由来のメチル基もポリシロキサン結合中に略均等に存在する。そして、反応がさらに進行すると、微細化されたポリシロキサン網目構造体が液中に分散した懸濁液の状態となる。

According to Scheme 2, the silanol group or ethoxy group of the siloxane oligomer reacts with the ethoxy group of methyltriethoxysilane, and the dealcoholization is performed to form a polysiloxane bond. Here, since the silanol group or ethoxy group of the siloxane oligomer is dispersed almost uniformly in the siloxane skeleton as described above, the reaction between the silanol group or ethoxy group of the siloxane oligomer and the ethoxy group of methyltriethoxysilane ( (Dealcoholization) is also considered to proceed substantially evenly. As a result, siloxane bonds derived from methyltriethoxysilane are formed almost uniformly in the generated polysiloxane bond, and therefore methyl groups derived from methyltriethoxysilane are also present almost uniformly in the polysiloxane bond. When the reaction further proceeds, a finely divided polysiloxane network structure is in a suspension state dispersed in the liquid.

  In the preparation step, the blending ratio (A2 / B2) of the tetraalkoxysilane (A2) and the hydrocarbon group-containing trialkoxysilane (B2) is 0/100 to 70 / weight ratio in addition to the first mixed liquid. A second mixed solution obtained by mixing alkoxysilane adjusted to 30 with an acid catalyst, water, and an organic solvent is further prepared. A 2nd liquid mixture is used in the below-mentioned "2nd application | coating process." Each compounding amount of alkoxysilane (tetraalkoxysilane and hydrocarbon group-containing trialkoxysilane), acid catalyst, water, and organic solvent is based on 1 mol of the total amount of tetraalkoxysilane and hydrocarbon group-containing trialkoxysilane. The acid catalyst is preferably adjusted to 0.005 to 0.1 mol, water 0.017 to 3 mol, and organic solvent 5 to 60 mol. When the compounding amount of the acid catalyst is less than 0.005 mol, the hydrolysis rate becomes low and the time required for producing the separation membrane becomes long. When the compounding amount of the acid catalyst is more than 0.1 mol, the hydrolysis rate becomes excessive, and it becomes difficult to obtain a uniform separation membrane. The blending amount of water is set to be smaller than that of the first mixed solution, but when the blending amount of water is less than 0.017 mol, the hydrolysis rate becomes small and the sol-gel reaction described later does not proceed sufficiently. When the amount of water is more than 3 mol, it becomes difficult to obtain a dense and uniform separation membrane. When the blending amount of the organic solvent is less than 5 mol, the concentration of the second mixed solution becomes high, and it becomes difficult to obtain a dense and uniform separation membrane. When the blending amount of the organic solvent is more than 60 mol, the concentration of the second mixed solution is lowered, the number of coating times (number of steps) of the mixed solution is increased, and the production efficiency is lowered. As the acid catalyst and the organic solvent, those similar to the first mixed liquid can be used. When preparing the second mixed solution, a metal salt having an affinity for carbon dioxide can be blended. The compounding amount of the metal salt is adjusted to 0.01 to 0.3 mol in the above compounding conditions. As the metal salt having an affinity for carbon dioxide, those described in the above item “Separation membrane for treatment of acid gas-containing gas” can be used. When a metal salt is added, it is considered that the metal salt taken into the polysiloxane during the sol-gel reaction is dispersed substantially evenly in the polysiloxane bond.

  In preparing the first mixed liquid and the second mixed liquid, the blending ratio (A1 / B1) at the time of preparing the first mixed liquid is larger than the blending ratio (A2 / B2) at the time of preparing the second mixed liquid. Thus, tetraalkoxysilane and hydrocarbon group-containing trialkoxysilane are blended. With such a composition, the separation membrane finally obtained contains more hydrocarbon groups derived from the hydrocarbon group-containing trialkoxysilane in the separation layer than in the intermediate layer. The balance between the separation performance and the film formability is good.

  The reaction of the second mixed solution is the same as in the above-described scheme 1 and scheme 2. The hydrolysis reaction that proceeds in the second mixed solution is referred to as “second hydrolysis reaction”. Here, when the first hydrolysis reaction and the second hydrolysis reaction are compared, the amount of water contained in the first mixed solution is set to be greater than the amount of water contained in the second mixed solution. The hydrolysis reaction has a higher hydrolysis rate than the second hydrolysis reaction. When the hydrolysis rate is increased, the polysiloxane network structure obtained by the sol-gel reaction is polymerized, and the surface of the inorganic porous support described later can be stabilized.

  Although the preparation step is performed as described above, in the preparation of the first mixed solution, it is preferable to mix water in a plurality of times. In this case, since the first hydrolysis reaction can surely proceed, the surface of the inorganic porous support can be further stabilized. In preparation of the first mixed liquid and the second mixed liquid, the acid catalyst should be mixed in a plurality of times, or the hydrocarbon group-containing trialkoxysilane which is easily hydrolyzed is mixed at the end. Is preferred. For example, the composition is prepared so that the pH of the mixed solution always falls within the range of 0.8 to 2.5. In this case, since the pH of the mixed solution does not vary greatly, hydrolysis of the hydrocarbon group-containing trialkoxysilane does not proceed rapidly, and the sol-gel reaction can proceed in a stable state. Furthermore, when the amount of water used for the preparation of the first mixed solution is W1 and the amount of water used for the preparation of the second mixed solution is W2, the ratio (W1 / W2) between them is 10 in terms of mole. It is preferable to set to ~ 20. In this case, the intermediate layer described later is further stabilized, and the gas selectivity and gas permeability of the separation layer formed on the intermediate layer can be improved.

(B) 1st application | coating process As a 1st application | coating process, the 1st liquid mixture (suspension of the refined | miniaturized polysiloxane network structure) obtained at the preparation process is apply | coated to an inorganic porous support body. Examples of the method for applying the first mixed liquid to the inorganic porous support include a dipping method, a spray method, and a spin method. Among these, the dipping method is a preferable coating method because the mixed solution can be uniformly and easily applied to the surface of the inorganic porous support. A specific procedure of the dipping method will be described.
First, the inorganic porous support is immersed in the first mixed solution. The dipping time is preferably 5 seconds to 10 minutes so that the first mixed liquid sufficiently adheres to the inorganic porous support. If the immersion time is shorter than 5 seconds, the film thickness is not sufficient, and if it exceeds 10 minutes, the film thickness becomes too large. Next, the inorganic porous support is pulled up from the first mixed solution. The pulling speed is preferably 0.1 to 2 mm / second. When the pulling speed is slower than 0.1 mm / second, the film thickness becomes too large, and when it is faster than 2 mm / second, the film thickness is not sufficient. Next, the pulled up inorganic porous support is dried. The drying conditions are preferably 15 to 40 ° C. and 0.5 to 3 hours. If the drying time is less than 0.5 hours, sufficient drying cannot be performed, and the drying state hardly changes even if the drying time exceeds 3 hours. When the drying is finished, a fine polysiloxane network structure adhered to the surface of the inorganic porous support (including the inner surfaces of some fine pores) is obtained. In addition, the adhesion amount of the refined | miniaturized polysiloxane network structure to an inorganic porous support body can be increased by repeating a series of procedures of immersion of an inorganic porous support body, pulling up, and drying several times. Moreover, since the first mixed liquid can be uniformly applied to the inorganic porous support by repeating a series of procedures, the finally obtained separation membrane for treatment of acid gas-containing gas can be further stabilized. .

(C) Intermediate layer forming step As the intermediate layer forming step, the inorganic porous support that has been subjected to the first coating step is heat-treated, and the refined polysiloxane network structure is fixed to the surface of the inorganic porous support. An intermediate layer mainly composed of a polysiloxane network structure is formed by fusing. For the heat treatment, for example, a heating means such as a calciner is used. A specific procedure for the heat treatment will be described.
First, the inorganic porous support is heated up to a heat treatment temperature described later. The temperature raising time is preferably 1 to 24 hours. If the temperature rising time is shorter than 1 hour, it is difficult to obtain a uniform film due to a rapid temperature change, and if it is longer than 24 hours, the film may be deteriorated by heating for a long time. After the temperature rise, heat treatment (firing) is performed for a certain time. The heat treatment temperature is preferably 30 to 300 ° C, more preferably 50 to 200 ° C. If the heat treatment temperature is lower than 30 ° C., sufficient heat treatment cannot be performed, so that a dense film cannot be obtained. If the heat treatment temperature is higher than 300 ° C., the film may be deteriorated by heating at a high temperature. The heat treatment time is preferably 0.5 to 6 hours. If the heat treatment time is shorter than 0.5 hours, sufficient heat treatment cannot be performed, so that a dense film cannot be obtained. If the heat treatment time is longer than 6 hours, the film may be deteriorated by heating for a long time. After the heat treatment is finished, the inorganic porous support is cooled to room temperature. The cooling time is preferably 5 to 10 hours. If the cooling time is shorter than 5 hours, the film may be cracked or peeled off due to a rapid temperature change, and if it is longer than 10 hours, the film may be deteriorated. An intermediate layer is formed on the surface of the inorganic porous support after cooling (including the inner surfaces of some of the micropores). The intermediate layer basis weight is adjusted to 0.1~4.0mg / cm ^2, it is preferably adjusted to 0.5-2.0 mg / cm ^2. After the “intermediate layer forming step”, the process returns to the “first applying step” described above, and the first applying step and the intermediate layer forming step are repeated as a set. In addition, an intermediate layer having a denser and uniform film quality can be formed.

(D) Second coating step As the second coating step, a second mixed liquid (suspension of the refined polysiloxane network structure) is applied to the inorganic porous support on which the intermediate layer has been formed by the intermediate layer forming step. Apply. Since the second mixed liquid applied in the second application step is applied to the inorganic porous support through the intermediate layer, the amount of penetration of the second mixed liquid into the inorganic porous support (inorganic porous The distance that the tetraalkoxysilane or hydrocarbon group-containing trialkoxysilane soaks in the depth direction from the surface of the support can be suppressed to 50 μm or less. Therefore, when the mixed gas is allowed to pass through the separation membrane for acid gas-containing gas treatment that has been completed by the separation layer forming step described later, the fine pores of the inorganic porous support are not clogged excessively. The throughput of the mixed gas) can be maintained. In addition, since the amount of the intermediate layer and separation layer forming material (sol) applied to the inorganic porous support can be reduced, the production cost of the separation membrane for acid gas-containing gas treatment can be reduced. . The method and conditions for applying the second mixed solution are the same as in the first application step. Also in the second coating step, a series of steps of immersing, pulling up, and drying the inorganic porous support in the second mixed solution is repeated a plurality of times, thereby refining the polysiloxane network structure on the inorganic porous support. The amount of body adhesion can be increased. Moreover, since the second mixed liquid can be uniformly applied to the inorganic porous support by repeating a series of procedures, the separation performance of the finally obtained separation membrane for treatment of acid gas-containing gas is further improved. be able to.

(E) Separation layer formation step As the separation layer formation step, the inorganic porous support having been subjected to the second coating step is heat-treated, and the refined polysiloxane network structure is fixed to the surface of the inorganic porous support. By fusing, a separation layer mainly comprising a polysiloxane network structure is formed. The heat treatment method and conditions are the same as those in the intermediate layer forming step. A separation layer is formed on the intermediate layer by the separation layer forming step. The separation layer has a basis weight adjusted to 0.1 to 3.0 mg / cm ² , preferably 0.3 to 1.5 mg / cm ² . After the “separation layer forming step”, the process returns to the “second application step” described above, and when the second coating step and the separation layer forming step are repeated as a set, the surface of the inorganic porous support is obtained. In addition, it is possible to form a separation layer having a finer and more uniform film quality.

  By carrying out the above steps (a) to (e), the separation membrane for treatment of acid gas-containing gas of the present invention having the intermediate layer and the separation layer is completed. In this separation membrane, a separation layer having a site (methyl group) that attracts a specific gas (carbon dioxide in this embodiment) is formed on an inorganic porous support as a base. The separation layer is formed on the surface of the inorganic porous support via the intermediate layer. Here, since the polysiloxane network structure contained in the intermediate layer contains a hydrocarbon group derived from the hydrocarbon group-containing trialkoxysilane, it has more flexibility than a general network structure. For this reason, the intermediate layer is improved in overall flexibility and flexibility while maintaining a certain degree of rigidity by the tetraalkoxysilane. When the flexibility of the intermediate layer is improved, the film formability of the intermediate layer is improved. Thereby, the crack and peeling of the intermediate layer are prevented, and the amount of the raw material liquid of the separation layer penetrating into the inorganic porous support is reduced. There is no problem as long as the amount of the raw material liquid soaked (distance to penetrate) is 50 μm or less, but preferably 20 μm or less. In this case, an increase in the thickness of the separation layer can be suppressed, and an acidic gas-containing gas treatment separation membrane excellent in gas permeability can be obtained.

  Moreover, the polysiloxane network structure contained in each of the intermediate layer and the separation layer is composed of materials of the same system except that the blending ratio of tetraalkoxysilane and hydrocarbon group-containing trialkoxysilane is different. , Have high affinity for each other. Therefore, interface peeling or cracking does not occur between the intermediate layer and the separation layer, and both are firmly adhered to each other, and a stable separation membrane for acid gas-containing gas treatment can be constituted.

  When a mixed gas containing acid gas such as carbon dioxide and methane gas is passed through the completed separation membrane for treatment of acid gas-containing gas, the separation layer is derived from hydrocarbon group-containing trialkoxysilane rather than the intermediate layer. Since it contains many hydrocarbon groups, the acidic gas in the mixed gas is selectively attracted to the separation layer and permeates the separation membrane as it is. As a result, the methane gas component in the mixed gas is concentrated, and high-concentration methane gas can be obtained efficiently. The concentrated methane gas can be used as a raw material for city gas and a raw material for hydrogen used in fuel cells. When the separation layer has a site that attracts methane gas (hydrocarbon group having an ethyl group or more carbon number), when a mixed gas containing carbon dioxide and methane gas is passed, the methane gas is selectively contained in the separation layer. Attracted, methane gas passes through the pores as they are. Therefore, in this case, methane gas that has permeated through the separation membrane can be recovered and used as a raw material for city gas or a raw material for hydrogen used in a fuel cell.

  In the separation membrane for acid gas-containing gas treatment, the mixing ratio (A1 / B1) of the tetraalkoxysilane (A1) and the hydrocarbon group-containing trialkoxysilane (B1) in the intermediate layer, and the tetraalkoxysilane (A2) in the separation layer And a hydrocarbon group-containing trialkoxysilane (B2) having various blending ratios (A2 / B2) were prepared, and a gas separation performance confirmation test was performed on each separation membrane. Furthermore, the structure of the separation membrane for acid gas-containing gas treatment was analyzed by a scanning electron microscope (SEM).

  An alumina-based ceramic tubular body having a tubular structure was used as an inorganic porous support in common to all separation membranes. The raw materials of the intermediate layer and the separation layer are tetraethoxysilane (Shin-Etsu Chemical LS-2430, manufactured by Shin-Etsu Chemical Co., Ltd.) as tetraalkoxysilane, and methyltriethoxysilane (Shin-Etsu Chemical Co., Ltd., Shin-Etsu Chemical) as a hydrocarbon group-containing trialkoxysilane. Silicone LS-1890), nitric acid (reagent special grade 69.5%, manufactured by Wako Pure Chemical Industries, Ltd.) as an acid catalyst, and ethanol (reagent special grade 99.5%, manufactured by Wako Pure Chemical Industries, Ltd.) were used as an organic solvent.

[Examples 1-6, Comparative Examples 1-5, Reference Example 1]
<Preparation of the first mixture>
A mixed solution of 0.007 g of nitric acid, 36.31 g of ethanol and 35.47 g of water was stirred for 30 minutes, and then 8.21 g of tetraethoxysilane was added and stirred for 2 hours, whereby an alkoxide solution for forming an intermediate layer (first A base solution of (mixed solution) was prepared. The pH of the base solution was 3.85. The molar concentration ratio of each component contained in the base solution is 0.003 for nitric acid, 20 for ethanol, and 50 for water, assuming that tetraethoxysilane is 1. Methyltriethoxysilane was added to 40 g of this base solution, and this was stirred for 2.5 hours to prepare an alkoxide solution for forming an intermediate layer (first mixed solution). The addition amount (content) of methyltriethoxysilane was set such that the ratio of methyltriethoxysilane in all alkoxysilanes contained in the first mixed solution was 0.5 to 60% by weight. Therefore, as shown in Table 1 below, the blending ratio (A1 / B1) of tetraethoxysilane (A1) and methyltriethoxysilane (B1) is 40/60 to 99.5 / 0.5 in weight ratio. Reference Example 1 (0% by weight) is a separation membrane corresponding to a conventional product not containing methyltriethoxysilane. In Table 1, tetraethoxysilane is represented as “TEOS” and methyltriethoxysilane is represented as “Me-TEOS”.

<Preparation of second mixed solution>
A mixed solution of 0.04 g of nitric acid, 63.16 g of ethanol and 2.47 g of water was stirred for 30 minutes, then 8.57 g of tetraethoxysilane was added and stirred for 1 hour, and then 4.89 g of methyltriethoxysilane was added. Then, 0.88 g of magnesium nitrate hexahydrate was added and the mixture was stirred for 2 hours to prepare an alkoxide solution for forming a separation layer (second mixed solution). The pH of the second mixed solution was 1.59. The molar concentration ratio of each component contained in the second liquid mixture is 0.01 for nitric acid, 20 for ethanol, 2 for water, 6 for magnesium nitrate, assuming that the total amount of tetraethoxysilane and methyltriethoxysilane is 1. Hydrate is 0.05. The proportion of methyltriethoxysilane in all alkoxysilanes contained in the second mixed solution was set to a constant 36% by weight. Therefore, as shown in Table 1 below, the blending ratio (A2 / B2) of tetraethoxysilane (A2) and methyltriethoxysilane (B2) is 64/36 by weight.

<Formation of intermediate layer and separation layer>
The first mixed liquid was applied to the surface of an alumina ceramic tubular body having a tubular structure by a dipping method. The lifting speed of the dipping method was 5 mm / s, and after the lifting, the film was dried at room temperature for 1 hour. After the application and drying of the first mixed solution was repeated twice, heat treatment was performed in a calciner. The heat treatment was performed by heating from room temperature (25 ° C.) to 150 ° C. over 5 hours, holding at 150 ° C. for 2 hours, and cooling to 25 ° C. over 5 hours. The above operation (coating) was repeated three times to form an intermediate layer on the surface of the tubular body. Next, the 2nd liquid mixture was apply | coated to the surface of the tubular body in which the intermediate layer was formed by the dipping method. The lifting speed of the dipping method was 5 mm / s, and after the lifting, the film was dried at room temperature for 1 hour. After the application and drying of the second mixed solution was repeated twice, heat treatment was performed in a calciner. The heat treatment was performed by heating from room temperature (25 ° C.) to 150 ° C. over 5 hours, holding at 150 ° C. for 2 hours, and cooling to 25 ° C. over 5 hours. The above operation (coating) was repeated twice to form a separation layer on the intermediate layer. In the above layer formation step, the intermediate layer and the separation layer in Examples 1 to 6 had no problem in film formability. Regarding the basis weight, as shown in Table 1 below, in each of Examples 1 to 6, the basis weight of the separation layer was smaller than the basis weight of the intermediate layer, and an increase in the thickness of the separation layer was suppressed. Regarding the basis weight of the intermediate layer, the basis weight was the same as that of the conventional product shown as Reference Example 1, and an acid gas-containing gas treatment separation membrane having a reduced thickness as a whole was obtained.

<Separation performance confirmation test>
Each separation membrane produced by the above procedure was subjected to a confirmation test regarding carbon dioxide separation performance. In this confirmation test, the gas permeation rate [P (N ₂ )] when nitrogen was permeated through the separation membrane and the gas permeation rate [P (CO ₂ )] when carbon dioxide was permeated through the same separation membrane were determined. It was measured. Here, the gas molecular diameter of nitrogen is 3.64 cm, and the gas molecular diameter of carbon dioxide is 3.3 cm. For this reason, carbon dioxide having a gas molecular diameter smaller than that of nitrogen easily passes through the separation membrane. Therefore, carbon dioxide can be separated from a mixed gas containing carbon dioxide by utilizing properties different depending on such gas and further appropriately setting the configuration of the membrane. In this confirmation test, the measurement of the gas permeation rate [P (CH ₃ )] when methane gas permeated through the separation membrane was not performed, but the gas molecule diameter of methane gas (3.8 cm) was the gas molecule of nitrogen. Since it is slightly larger than the diameter (3.64 mm), if it can be confirmed that carbon dioxide and nitrogen can be separated by the separation membrane of the present invention, it is estimated that carbon dioxide and methane gas can also be separated.

  FIG. 1 is a schematic configuration diagram of a gas permeation rate measuring apparatus 10 used in a separation performance confirmation test. The gas transmission rate measuring device 10 includes a gas cylinder 1, a pressure gauge 2, a chamber 3, and a mass flow meter 4. The separation membrane 5 is installed inside the chamber 3.

Carbon dioxide or nitrogen, which is a measurement gas, is filled in the gas cylinder 1 in advance. Here, it demonstrates as what filled the gas cylinder 1 with the carbon dioxide. The pressure of the carbon dioxide discharged from the gas cylinder 1 is adjusted by the pressure gauge 2 and supplied to the chamber 3 on the downstream side. In this confirmation test, the supply pressure of carbon dioxide was adjusted to 0.1 MPa at room temperature. The separation membrane 5, which is a tubular body, has one end (front end side) 5 a sealed and the other end (base end side) 5 b connected to the heat resistant glass tube 6. As the heat-resistant glass tube 6, a Pyrex (registered trademark) tube (an outer diameter of 8 mm, an inner diameter of 6 mm, and a length of 10 mm) manufactured by Corning was used. However, one end side of the heat-resistant glass tube 6 is reduced in diameter so that the outer diameter is 7 mm or less so that it can be inserted into the separation membrane 5 (inner diameter 7 mm). The connection between the separation membrane 5 and the heat-resistant glass tube 6 is bonded with an adhesive (adhesive “Cemedine (registered trademark) C” manufactured by Cemedine Co., Ltd.), and further an epoxy resin (two liquid manufactured by Nagase ChemteX Corporation). Adhesive epoxy adhesives “AV138” and “HV998”). When the chamber 3 is filled with carbon dioxide, the carbon dioxide permeates into the tube from the surface of the separation membrane 5 which is a tubular body, passes through the heat-resistant glass tube 6 and flows into the mass flow meter 4. As the mass flow meter 4, a thermal mass flow meter (mass flow meter “5410”) manufactured by Cofrock was used. The measurement conditions were a flow rate range of 10 mL / min and an accuracy with respect to the full-scale (FS) maximum flow rate of ± 1% (20 ° C.). From the flow rate [mL / min] of carbon dioxide measured with the mass flow meter 4, the gas permeation rate of carbon dioxide [P (CO ₂ )] (m ³ / (m ² × s (seconds) × Pa)) was calculated. . For nitrogen, the gas permeation rate [P (N ₂ )] (m ³ / (m ² × s (seconds) × Pa)) was calculated by the same procedure as described above. The carbon dioxide gas permeation rate [P (CO ₂ )] and the nitrogen gas permeation rate [P (N ₂ )] are compared with the permeation rate ratio [α (CO ₂ / N ₂ )]. Separation performance was evaluated. The results of the separation performance confirmation test are also shown in Table 1 described above.

The compounding ratio (A1 / B1) of tetraethoxysilane (A1) and methyltriethoxysilane (B1) is larger than the compounding ratio (A2 / B2) of tetraethoxysilane (A2) and methyltriethoxysilane (B2). The separation membranes of Examples 1 to 6 which were set had a large permeation rate ratio [α (CO ₂ / N ₂ )] between carbon dioxide and nitrogen, and were excellent in carbon dioxide separation performance. In contrast, in the separation membranes of Comparative Examples 1 to 5 in which the blending ratio (A1 / B1) is smaller than the blending ratio (A2 / B2), the permeation rate ratio [α (CO ₂ / N ₂ )] is small, A practical level of carbon dioxide separation performance was not achieved. Incidentally, the separation performance of carbon dioxide was also insufficient for Reference Example 1 in which methyltriethoxysilane was not included in the intermediate layer.

[Examples 7 to 9]
<Influence of preparation conditions of first mixture>
Next, when the preparation conditions of the first mixed solution were changed, the influence on the film forming property and separation performance of the separation membrane for acid gas-containing gas treatment was examined. The first mixed liquids of Examples 7 to 9 in Table 2 below have substantially the same composition as the first mixed liquid of Example 5 in Table 1, but the water addition conditions and stirring conditions were changed. doing. The numerical value (mole) in parentheses in the column of “water” in Table 2 is the molar concentration ratio of water when tetraethoxysilane is 1. In Examples 7 to 9, the proportions of methyltriethoxysilane in all alkoxysilanes contained in the first mixed solution were all set to a constant 28% by weight. That is, the compounding ratio (A1 / B1) of tetraethoxysilane (A1) and methyltriethoxysilane (B1) is 72/28. In addition, the ratio of methyltriethoxysilane in all alkoxysilanes contained in the second mixed solution was set to a constant 36% by weight. That is, the compounding ratio (A2 / B2) of tetraethoxysilane (A2) and methyltriethoxysilane (B2) is 64/36.

  In Example 7, a mixed solution of 0.0037 g of nitric acid, 22.7 g of ethanol and 22.17 g of water was stirred for 30 minutes, then 5.13 g of tetraethoxysilane was added and stirred for 2 hours, and further 2 g of methyltriethoxysilane was added. Was added and stirred for 2.5 hours to prepare a first mixed solution. Example 7 was prepared under the same conditions as in Example 5.

  In Example 8, a mixed solution of 0.0037 g of nitric acid, 22.7 g of ethanol and 0.89 g of water was stirred for 30 minutes, then 5.13 g of tetraethoxysilane was added and stirred for 2 hours, and then 2 g of methyltriethoxysilane was added. Was added and stirred for 2.5 hours, and 21.28 g of water was further added and stirred for 2 hours to prepare a first mixed solution. Example 8 is prepared by dividing the addition of water into Example 2 twice.

  In Example 9, a mixed solution of 0.0037 g of nitric acid, 22.7 g of ethanol and 0.89 g of water was stirred for 30 minutes, then 5.13 g of tetraethoxysilane was added and stirred for 1 hour, and then 2 g of methyltriethoxysilane was added. Was added and stirred for 2.5 hours, and 21.28 g of water was further added and stirred for 2 hours to prepare a first mixed solution (Example 9). Example 9 was prepared by reducing the stirring time after adding tetraethoxysilane to Example 8 to 1/2 of 1 hour.

In Examples 7 to 9, as in Examples 1 to 6, the intermediate layer and the separation layer had no problem in film formability. Regarding the basis weight, in all cases, the basis weight of the separation layer was smaller than the basis weight of the intermediate layer, and an increase in the thickness of the separation layer was suppressed. As a result, an acidic gas-containing gas treatment separation membrane having a reduced thickness as a whole was obtained. Regarding the performance of the separation membrane, the permeation rate ratio [α (CO ₂ / N ₂ )] between carbon dioxide and nitrogen was sufficiently large, and it was confirmed that the separation performance of carbon dioxide reached a practical level. In particular, Example 8 in which the addition of water was divided resulted in better separation performance than Example 7, and Example 9 in which the stirring time was shortened was even better than Example 8.

[Examples 10-11, Comparative Examples 6-8]
<Influence of hydrocarbon group-containing trialkoxysilane content>
Next, when the content of methyltriethoxysilane in all alkoxysilanes contained in the first mixed solution is greatly changed, the influence on the film formability and separation performance of the separation membrane for gas treatment containing acid gas investigated. In Examples 10 to 11 and Comparative Examples 6 to 7 in Table 3 below, the total amount of tetraethoxysilane and methyltriethoxysilane is 1 mol, and methyltriethoxysilane in all alkoxysilanes in the first mixed solution The ratio is adjusted to 60 to 80% by weight. In Comparative Example 8, the total amount of tetraethoxysilane and methyltriethoxysilane was 1 mol, and the ratio of methyltriethoxysilane in all alkoxysilanes in the first mixed liquid was adjusted to 0.01% by weight. is there. In Examples 10 to 11 and Comparative Examples 6 to 8, the preparation procedures of the first mixed solution and the second mixed solution, and the conditions for forming the intermediate layer and the separation layer on the support surface were the same as in Examples 1 to 6. is there.

In Examples 10 to 11, as in Examples 1 to 6, the intermediate layer and the separation layer had no problem in film formability. Regarding the basis weight, in all cases, the basis weight of the separation layer was smaller than the basis weight of the intermediate layer, and an increase in the thickness of the separation layer was suppressed. As a result, an acidic gas-containing gas treatment separation membrane having a reduced thickness as a whole was obtained. Regarding the performance of the separation membrane, the permeation rate ratio [α (CO ₂ / N ₂ )] between carbon dioxide and nitrogen was slightly smaller than in Examples 1 to 9, but better results were obtained compared to Comparative Example 6. When the content of methyltriethoxysilane in all the alkoxysilanes contained in the first mixed liquid was 70% or less, the possibility of use at a practical level was suggested. In the separation membrane of Comparative Example 7, the blending ratio (A1 / B1) of tetraethoxysilane (A1) and methyltriethoxysilane (B1) is blended of tetraethoxysilane (A2) and methyltriethoxysilane (B2). Since it is smaller than the ratio (A2 / B2), the basis weight of the intermediate layer is increased, and the film thickness of the intermediate layer is increased. As a result, the permeation rate ratio [α (CO ₂ / N ₂ )] was reduced, and the carbon dioxide separation performance was less than half that of the separation membranes of Examples 10-11. As for the separation membrane of Comparative Example 8, the content of methyltriethoxysilane in all the alkoxysilanes in the first mixed solution is extremely small, so that the film formability of the intermediate layer is poor and the carbon dioxide separation performance is poor. It became.

<Structural evaluation of intermediate layer>
The separation membrane for acid gas-containing gas treatment of the present invention is observed with a scanning electron microscope (SEM), and the content of the Si component is line-analyzed from the surface to the inner porous support. The soaking state of the first mixed liquid (intermediate layer) / second mixed liquid (separated layer) was evaluated.

  FIG. 2 is a graph showing the Si distribution of an acid gas-containing gas treatment separation membrane prepared by changing the amount of water added in the first mixed solution. (A) is a test specimen in which the amount of water added is 10 times the molar amount of tetraethoxysilane (molar concentration ratio), and (b) is the amount of water added 50 times the amount of tetraethoxysilane added. It is the test body made into (molar concentration ratio). It was found that as the amount of water added increases, the peak shape of the Si distribution becomes sharper and the penetration depth of the mixed solution into the inorganic porous support becomes shallower. Therefore, when a sol-gel reaction involving a hydrolysis reaction is allowed to proceed under conditions where a large amount of water is present, the hydrolysis reaction surely proceeds and the polysiloxane network structure is polymerized, resulting in an inorganic porous support. It is considered that a structure that stays in the vicinity of the surface of the film and hardly penetrates into the second mixed solution is obtained. Incidentally, in the case of forming the separation layer directly without forming the intermediate layer on the surface of the inorganic porous support, as shown in (c), the peak shape of the Si distribution becomes broad and the penetration depth is large. became.

  FIG. 3 is a graph showing the Si distribution of an acid gas-containing gas treatment separation membrane prepared by changing the addition conditions of water in the first mixed solution. (A) is a test body to which water was added at once, and (b) is a test body to which water was added in two portions. It was found that when water was added in two portions, the peak shape of the Si distribution became sharper and the penetration depth of the mixed solution into the inorganic porous support became shallower. From this, when preparing the first mixed solution, when water is divided into several times and mixed, the sol-gel reaction accompanied by hydrolysis reaction proceeds gently. It is considered that ethoxysilane is polymerized in a chain form, and then, as a second step, the polymer chains are combined to further enlarge the polysiloxane network structure. As a result, it is considered that the second mixed liquid is more difficult to penetrate into the inorganic porous support.

  The separation membrane for treatment of acid gas-containing gas and the production method thereof of the present invention can be used in city gas production facilities, hydrogen supply facilities for fuel cells, factory exhaust gas purification facilities, liquefied carbon dioxide production facilities, and the like. . It can also be used in CCS, which is being studied as a countermeasure against global warming.

DESCRIPTION OF SYMBOLS 1 Gas cylinder 2 Pressure gauge 3 Chamber 4 Mass flow meter 5 Separation membrane 6 Heat-resistant glass tube 10 Gas permeation rate measuring device

Claims (10)

A separation membrane for gas treatment containing an acidic gas, wherein an intermediate layer and a separation layer are laminated on an inorganic porous support,
In the intermediate layer, the blending ratio (A1 / B1) of the tetraalkoxysilane (A1) and the hydrocarbon group-containing trialkoxysilane (B1) was adjusted to 30/70 to 99.9 / 0.1 by weight. A polysiloxane network obtained by a sol-gel reaction of alkoxysilane,
The separation layer is an alkoxysilane sol in which the mixing ratio (A2 / B2) of the tetraalkoxysilane (A2) to the hydrocarbon group-containing trialkoxysilane (B2) is adjusted to 0/100 to 70/30 by weight ratio. -Comprising a polysiloxane network obtained by gel reaction,
The said mixing ratio (A1 / B1) is a separation membrane for acidic gas containing gas processing set larger than the said mixing ratio (A2 / B2). The tetraalkoxysilane is tetramethoxysilane or tetraethoxysilane,
The said hydrocarbon group containing trialkoxysilane is an acid gas containing gas treatment according to claim 1, wherein the alkyl group or phenyl group having 1 to 6 carbon atoms is bonded to Si atom of trimethoxysilane or triethoxysilane. Separation membrane.   The separation membrane for acid gas-containing gas treatment according to claim 1 or 2, wherein a metal salt having an affinity for acid gas is added to the separation layer.   The metal salt is an acetate, nitrate, carbonate, borate, or phosphoric acid of at least one metal selected from the group consisting of Li, Na, K, Cs, Mg, Ca, Ni, Fe, and Al. The separation membrane for acid gas-containing gas treatment according to claim 3, which is a salt. The weight of the intermediate layer is 0.1 to 4.0 mg / cm ² ,
The basis weight of the separating layer, acid gas-containing gas treating separation membrane according to claim 1 which is 0.1-3.0 mg / cm ^2.   The said inorganic porous support body is a separation membrane for acidic gas containing gas treatment as described in any one of Claims 1-5 which has a 4-200 nm micropore.   The separation membrane for acid gas-containing gas treatment according to any one of claims 1 to 6, wherein a distance from which the alkoxysilane penetrates in a depth direction from the surface of the inorganic porous support is 50 µm or less. (A) Alkoxysilane whose blending ratio (A1 / B1) of tetraalkoxysilane (A1) to hydrocarbon group-containing trialkoxysilane (B1) is adjusted to 30/70 to 99.9 / 0.1 by weight ratio , An acid catalyst, water, and a first mixed liquid in which an organic solvent is mixed, and a mixing ratio (A2 / B2) of the tetraalkoxysilane (A2) to the hydrocarbon group-containing trialkoxysilane (B2) is 0 / weight ratio. A second mixed solution in which an alkoxysilane adjusted to 100 to 70/30, an acid catalyst, water, and an organic solvent are mixed (wherein the blending ratio (A1 / B1) is based on the blending ratio (A2 / B2)). A preparation step for preparing a large set),
(B) a first coating step of coating the first mixed liquid on the surface of the inorganic porous support;
(C) an intermediate layer forming step of heat-treating the inorganic porous support after the first coating step is completed, and forming an intermediate layer including a polysiloxane network structure on the surface of the inorganic porous support;
(D) a second coating step of coating the second mixed solution on the intermediate layer;
(E) a separation layer forming step of heat-treating the inorganic porous support having undergone the second coating step to form a separation layer containing a polysiloxane network structure on the intermediate layer;
The manufacturing method of the separation membrane for acidic gas containing gas processing including this.   In the preparation step, the ratio (W1 / W2) between the amount of water (W1) used for preparing the first mixed solution and the amount of water (W2) used for preparing the second mixed solution is mol. The manufacturing method of the separation membrane for acidic gas containing gas processing of Claim 8 set to 10-20 in conversion.   The method for producing a separation membrane for acid gas-containing gas treatment according to claim 8 or 9, wherein water is divided into a plurality of times when the first mixed solution is prepared in the preparing step.

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